1. Field of the Invention
The present invention relates to a gas flow rate control system with an electromagnetic solenoid valve, which is designed to continuously and accurately control the extent of opening of the solenoid valve, whereby the reliability of the temperature control is improved.
2. Description of the Prior Art
Recently, energy saving has increasingly been one of the most urgent questions in daily life in connection with the oil crisis that the world's countries confront, and in this respect, there is the requirement or order set in motion, as one of the essential countermeasures for energy savings, to set a guide line for the proper heating temperatures at business offices and general households. It has often come into question that there are many facilities such as business offices, department stores or the like which are heated at much higher temperatures than necessary, and thus wastefully consuming valuable energy resources such as the fuel gas, etc. Under these circumstances, energy saving is essentially directed to the elimination of such wastefulness in the heating of buildings and housing by defining the heating temperature at a relatively low or moderate level.
For observing such a guideline of a moderate heating temperature, it is somehow essential to constantly monitor the room temperatures and positively control the supply rate of fuel gas for heating. In this connection, if the control system turns out to be too expensive, it is natural that the users would suffer from a substantial economical burden and thus such an expensive system could not be adopted in common use. As a consequence, it is required that such a system which is operable with ease and accuracy would be marketed at as low a price as possible. The conventional control system is of a construction in which an electromagnet or solenoid valve is incorporated for the control of room temperatures by turning the supply of fuel gas on or off in accordance with a current room temperature. Although these electromagnet valves are generally advantageous in being low cost, it is inevitable that the room temperature repeatedly goes up-and-down rather than remaining constant with such on and off switching of the electromagnetic valve. In this consideration, there has been proposed the arrangement such that an electromagnet valve that is less expensive in cost is adopted so as to have its opening controlled in a continual mode instead of in the on and off switching mode.
This continual control mode of the electromagnet valve that has now been made available is generally attained through the improvement on the part of the valve per se. It is generally known that when the plunger for driving a valve stem is controlled with the intensity of the energizing current of the solenoid or energizing coil, the plunger is magnetically attracted by a magnet yoke so as to contact therewith; therefore, the plunger would start its motion by overcoming a static friction force caused therebetween. In this condition, the plunger would naturally start its jumping motion as the very moment that the magnetic attraction from the solenoid overcomes the static friction force. In order to prevent such a quick motion, there is proposed such a construction that the plunger is held in a neutral position by using such an aid as a leaf spring, so as to provide a space between the plunger and the magnet yoke. Such an arrangement, would disadvantageously provide an added magnetic reluctance, and it is inevitable that the solenoid is designed to be larger to a certain extent than otherwise required, and also the energizing current is increased substantially. In addition, there is such a disadvantage that due to the hysteresis of the magnetic material constituting the magnetic circuit, such as plunger and yoke, there would occur an unequal opening of the valve when powered in its opening direction versus its closing direction with an equal driving current. As a consequence thereof, it is unavoidable that there would eventually occur an uncontrolled extent of deviation between a current ambient temperature and an opening of the valve, and this particular extent of deviation would not be consistent.
It is also known that there is proposed such measures for coping with such undesirable problem as mentioned above by disposing a moving coil which is provided in a floating relationship with a ring-shaped permanent magnet for the purpose of driving the valve stem. However, this arrangement cannot be relieved from such disadvantages that the permanent magnet would change its performance characteristics when given an impact and that it needs lead connection to its moving coil; it would therefore become complex in construction and hence expensive in its manufacturing cost.